Ok back to topic 8]
FS keeped on crashing during the game with my UAC turned on...
so i decided to give it a try BUT didnt want to shut down the secruity system (UAC) which -so far- didnt cause any problems.
So i goggled a bit and found amongst many posts and tools a nice work around to turn off UAC for a specific service which uses the help of an official microsoft tool called "Microsoft Application Compatibility Toolkit 5.0"....*cough*...well, that shouldnt be too bad 
anyways.....i found a very good description how to disable UAC for FirstStrike, which isnt very difficult and veeeeeeeery helpful 8)
BUT....
its in german ;P
www.vs-support.com/tipps_tricks/uac.htm
in summary all you have to do is to install the tool, create a new database for an application (FirstStrike.exe), click "none" when asked for compability modi and check "run as invoker"
then SAVE the database, name it and place the file wherever you prefer
the last you have to do then is to tell windows that there is a new database by opening DOS-window
and the command SDBINST followed by a gap and then the path to your database you just created
i saved my database (FSfix_UACoff.sdb) in the Battlefield2142 root folder so f.ex. my command line is
SDBINST C:\Spielhalle\bf2142\FSfix_UACoff.sdb
since then FS didnt crash anymore and finally i can enjoy FS again 